Inbred corn line LH172

ABSTRACT

An inbred corn line, designated LH172, is disclosed. The invention relates to the seeds of inbred corn line LH172, to the plants of inbred corn line LH172 and to methods for producing a corn plant produced by crossing the inbred line LH172 with itself or another corn line. The invention further relates to hybrid corn seeds and plants produced by crossing the inbred line LH172 with another corn line.

BACKGROUND OF THE INVENTION

The present invention relates to a new and distinctive corn inbred line, designated LH172. There are numerous steps in the development of any novel, desirable plant germplasm. Plant breeding begins with the analysis and definition of problems and weaknesses of the current germplasm, the establishment of program goals, and the definition of specific breeding objectives. The next step is selection of germplasm that possess the traits to meet the program goals. The goal is to combine in a single variety or hybrid an improved combination of desirable traits from the parental germplasm. These important traits may include higher yield, resistance to diseases and insects, better stalks and roots, tolerance to drought and heat, and better agronomic quality.

Choice of breeding or selection methods depends on the mode of plant reproduction, the heritability of the trait(s) being improved, and the type of cultivar used commercially (e.g., F₁ hybrid cultivar, pureline cultivar, etc.). For highly heritable traits, a choice of superior individual plants evaluated at a single location will be effective, whereas for traits with low heritability, selection should be based on mean values obtained from replicated evaluations of families of related plants. Popular selection methods commonly include pedigree selection, modified pedigree selection, mass selection, and recurrent selection.

The complexity of inheritance influences choice of the breeding method. Backcross breeding is used to transfer one or a few favorable genes for a highly heritable trait into a desirable cultivar. This approach has been used extensively for breeding disease-resistant cultivars. Various recurrent selection techniques are used to improve quantitatively inherited traits controlled by numerous genes. The use of recurrent selection in self-pollinating crops depends on the ease of pollination, the frequency of successful hybrids from each pollination, and the number of hybrid offspring from each successful cross.

Each breeding program should include a periodic, objective evaluation of the efficiency of the breeding procedure. Evaluation criteria vary depending on the goal and objectives, but should include gain from selection per year based on comparisons to an appropriate standard, overall value of the advanced breeding lines, and number of successful cultivars produced per unit of input (e.g., per year, per dollar expended, etc.).

Promising advanced breeding lines are thoroughly tested and compared to appropriate standards in environments representative of the commercial target area(s) for three years at least. The best lines are candidates for new commercial cultivars; those still deficient in a few traits are used as parents to produce new populations for further selection.

These processes, which lead to the final step of marketing and distribution, usually take from eight to 12 years from the time the first cross is made. Therefore, development of new cultivars is a time-consuming process that requires precise forward planning, efficient use of resources, and a minimum of changes in direction.

A most difficult task is the identification of individuals that are genetically superior, because for most traits the true genotypic value is masked by other confounding plant traits or environmental factors. One method of identifying a superior plant is to observe its performance relative to other experimental plants and to a widely grown standard cultivar. If a single observation is inconclusive, replicated observations provide a better estimate of its genetic worth.

The goal of plant breeding is to develop new, unique and superior corn inbred lines and hybrids. The breeder initially selects and crosses two or more parental lines, followed by repeated selfing and selection, producing many new genetic combinations. The breeder can theoretically generate billions of different genetic combinations via crossing, selfing and mutations. The breeder has no direct control at the cellular level. Therefore, two breeders will never develop the same line, or even very similar lines, having the same corn traits.

Each year, the plant breeder selects the germplasm to advance to the next generation. This germplasm is grown under unique and different geographical, climatic and soil conditions, and further selections are then made, during and at the end of the growing season. The inbred lines which are developed are unpredictable. This unpredictability is because the breeder's selection occurs in unique environments, with no control at the DNA level (using conventional breeding procedures), and with millions of different possible genetic combinations being generated. A breeder of ordinary skill in the art cannot predict the final resulting lines he develops, except possibly in a very gross and general fashion. The same breeder cannot produce the same line twice by using the exact same original parents and the same selection techniques. This unpredictability results in the expenditure of large research monies to develop a superior new corn inbred line.

The development of commercial corn hybrids requires the development of homozygous inbred lines, the crossing of these lines, and the evaluation of the crosses. Pedigree breeding and recurrent selection breeding methods are used to develop inbred lines from breeding populations. Breeding programs combine desirable traits from two or more inbred lines or various broad-based sources into breeding pools from which inbred lines are developed by selfing and selection of desired phenotypes. The new inbreds are crossed with other inbred lines and the hybrids from these crosses are evaluated to determine which have commercial potential.

Pedigree breeding is used commonly for the improvement of self-pollinating crops or inbred lines of cross-pollinating crops. Two parents which possess favorable, complementary traits are crossed to produce an F₁. An F₂ population is produced by selfing one or several F₁ 's or by intercrossing two F₁ 's (sib mating). Selection of the best individuals is usually begun in the F₂ population; then, beginning in the F₃, the best individuals in the best families are selected. Replicated testing of families, or hybrid combinations involving individuals of these families, often follows in the F₄ generation to improve the effectiveness of selection for traits with low heritability. At an advanced stage of inbreeding (i.e., F₆ and F₇), the best lines or mixtures of phenotypically similar lines are tested for potential release as new cultivars.

Mass and recurrent selections can be used to improve populations of either self- or cross-pollinating crops. A genetically variable population of heterozygous individuals is either identified or created by intercrossing several different parents. The best plants are selected based on individual superiority, outstanding progeny, or excellent combining ability. The selected plants are intercrossed to produce a new population in which further cycles of selection are continued.

Backcross breeding has been used to transfer genes for a simply inherited, highly heritable trait into a desirable homozygous cultivar or inbred line which is the recurrent parent. The source of the trait to be transferred is called the donor parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent. After the initial cross, individuals possessing the phenotype of the donor parent are selected and repeatedly crossed (backcrossed) to the recurrent parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent.

Descriptions of the other breeding methods that are commonly used for different traits and crops can be found in one of several reference books (e.g., Allard, 1960; Simmonds, 9; Sneep et al., 9; Fehr, 1987).

Proper testing should detect any major faults and establish the level of superiority or improvement over current cultivars. In addition to showing superior performance, there must be a demand for a new cultivar that is compatible with industry standards or which creates a new market. The introduction of a new cultivar will incur additional costs to the seed producer, the grower, processor and consumer; for special advertising and marketing, altered seed and commercial production practices, and new product utilization. The testing preceding release of a new cultivar should take into consideration research and development costs as well as technical superiority of the final cultivar. For seed-propagated cultivars, it must be feasible to produce seed easily and economically.

Once the inbreds that give the best hybrid performance have been identified, the hybrid seed can be reproduced indefinitely as long as the homogeneity of the inbred parent is maintained. A single-cross hybrid is produced when two inbred lines are crossed to produce the F₁ progeny. A double-cross hybrid is produced from four inbred lines crossed in pairs (A×B and C×D) and then the two F₁ hybrids are crossed again (A×B)×(C×D). Much of the hybrid vigor exhibited by F₁ hybrids is lost in the next generation (F₂). Consequently, seed from hybrid varieties is not used for planting stock.

Corn is an important and valuable field crop. Thus, a continuing goal of plant breeders is to develop stable, high yielding corn hybrids that are agronomically sound. The reasons for this goal are obviously to maximize the amount of grain produced on the land used and to supply food for both animals and humans. To accomplish this goal, the corn breeder must select and develop corn plants that have the traits that result in superior parental lines for producing hybrids.

SUMMARY OF THE INVENTION

According to the invention, there is provided a novel inbred corn line, designated LH172. This invention thus relates to the seeds of inbred corn line LH172, to the plants of inbred corn line LH172 and to methods for producing a corn plant produced by crossing the inbred line LH172 with itself or another corn line. This invention further relates to hybrid corn seeds and plants produced by crossing the inbred line LH172 with another corn line.

DEFINITIONS

In the description and tables which follows, a number of terms are used. In order to provide a clear and consistent understanding of the specification and claims, including the scope to be given such terms, the following definitions are provided:

Predicted RM. This trait for a hybrid, predicted relative maturity (RM), is based on the harvest moisture of the grain. The relative maturity rating is based on a known set of checks and utilizes conventional maturity systems such as the Minnesota Relative Maturity Rating System.

MN RM. This represents the Minnesota Relative Maturity Rating (MN RM) for the hybrid and is based on the harvest moisture of the grain relative to a standard set of checks of previously determined MN RM rating. Regression analysis is used to compute this rating.

Yield (Bushels/Acre). The yield in bushels/acre is the actual yield of the grain at harvest adjusted to 15.5% moisture.

Moisture. The moisture is the actual percentage moisture of the grain at harvest.

GDU Silk. The GDU silk (=heat unit silk) is the number of growing degree units (GDU) or heat units required for an inbred line or hybrid to reach silk emergence from the time of planting. Growing degree units are calculated by the Barger Method, where the heat units for a 24-hour period are: ##EQU1## The highest maximum used is 86° and the lowest minimum used is 50° F. For each hybrid, it takes a certain number of GDUs to reach various stages of plant development. GDUs are a way of measuring plant maturity.

Stalk Lodging. This is the percentage of plants that stalk lodge, i.e., stalk breakage, as measured by either natural lodging or pushing the stalks determining the percentage of plants that break off below the ear. This is a relative rating of a hybrid to other hybrids for standability.

Root Lodging. The root lodging is the percentage of plants that root lodge; i.e., those that lean from the vertical axis at an approximate 30° angle or greater would be counted as root lodged.

Plant Height. This is a measure of the height of the hybrid from the ground to the tip of the tassel, and is measured in centimeters.

Ear Height. The ear height is a measure from the ground to the ear node attachment, and is measured in centimeters.

Dropped Ears. This is a measure of the number of dropped ears per plot, and represents the percentage of plants that dropped an ear prior to harvest.

DETAILED DESCRIPTION OF THE INVENTION

Inbred corn line LH172 is a yellow dent corn with superior characteristics, and provides an excellent parental line in crosses for producing first generation (F₁) hybrid corn.

Inbred corn line LH172 was developed from the cross (LH82×LH122)×LH82 by selfing and using the ear-row pedigree method of breeding. Selfing and selection were practiced within the above F₁ cross for six generations in the development of LH172. During the development of the line, crosses were made to inbred testers for the purpose of estimating the line's general and specific combining ability, and evaluations were run by the Williamsburg, Iowa Research Station. The inbred was evaluated further as a line and in numerous crosses by the Williamsburg Research Station and other research stations across the Corn Belt. The inbred has proven to have a very good combining ability in hybrid combinations, and makes an excellent female seed parent.

The inbred has shown uniformity and stability for all traits, as described in the following variety description information. It has been self-pollinated and ear-rowed a sufficient number of generations, with careful attention to uniformity of plant type to ensure homozygosity and phenotypic stability. The line has been increased both by hand and sibbed in isolated fields with continued observation for uniformity. No variant traits have been observed or are expected in LH172.

Inbred corn line LH172 has the following morphologic and other characteristics (based primarily on data collected at Williamsburg, Iowa):

VARIETY DESCRIPTION INFORMATION

A. Maturity

INBRED=LH172

Best Adapted For: Most Regions of Corn Belt

Heat Unit Silk: 1400 ##EQU2##

B. Plant Characteristics

Plant height (to tassel tip): 152 cm.

Length of top ear internode: 11 cm.

Number of ears per stalk: Strong two-ear tendency

Ear height (to base of top ear): 65 cm.

Number of tillers: None

Cytoplasm type: Normal

C. Leaf

Color: 5 GY 4/6 Munsell Color Charts for Plant Tissue

Angle from stalk: 30°-60°

Marginal waves: few

Number of leaves (mature plants): 11

Sheath pubescence: Light

Longitudinal creases: Few

Length (ear node leaf): 66 cm.

Width (widest point of ear node leaf): 12 cm.

D. Tassel

Number of lateral branches: 5

Branch angle from central spike: <30°

Pollen shed: Heavy

Peduncle length (top leaf to basal branch): 2 cm.

Anther color: Purple

Glume color: Green

E. Ear (Husked Ear Data Except When Stated Otherwise)

Length: 16 cm.

Weight: 79 gm.

Midpoint diameter: 44 mm.

Silk color: Green

Husk extension: Medium (barely covering ear)

Husk leaf: <8 cm.

Taper of Ear: Slight

Position of shank (dry husks): Upright

Kernel rows: 16

Husk color (fresh): Light green

Husk color (dry): Buff

Shank length: 11 cm.

Shank (no. of internodes): 9

F. Kernel (Dried)

Size (from ear midpoint)

Length: 11 mm.

Width: 8 mm.

Thickness: 4 mm.

Shape grade (% rounds): 60-80

Pericarp color: Colorless

Aleurone color: White

Endosperm color: Yellow

Endosperm type: Normal starch

Gm Weight/100 seeds (unsized): 28 gm.

G. Cob

Diameter at midpoint: 33 mm.

Strength: Strong

Color: Red

H. Disease Resistance

N. Turcicum Race 1 (Northern Leaf Blight): tolerant

This invention is also directed to methods for producing a corn plant by crossing a first parent corn plant with a second parent corn plant, wherein the first or second corn plant is the inbred corn plant from the line LH172. Further, both first and second parent corn plants may be from the inbred line LH172. Therefore, any methods using the inbred corn line LH172 are part of this invention: selfing, backcrosses, hybrid breeding, and crosses to populations. Any plants produced using inbred corn line LH172 as a parent are within the scope of this invention. Advantageously, the inbred corn line is used in crosses with other corn varieties to produce first generation (F₁) corn hybrid seed and plants with superior characteristics.

As used herein, the term "plant" includes plant cells, plant protoplasts, plant cell of tissue culture from which corn plants can be regenerated, plant calli, plant clumps, and plant cells that are intact in plants or parts of plants, such as pollen, flowers, kernels, ears, cobs, leaves, husks, stalks, and the like.

Tissue culture of corn is described in European Patent Application, Publication No. 160,390. Corn tissue culture procedures are also described in Green and Rhodes, "Plant Regeneration in Tissue Culture of Maize", Maize for Biological Research (Plant Molecular Biology Association, Charlottesville, Va. 1982), at 367-372. Thus, another aspect of this invention is to provide for cells which upon growth and differentiation produce the inbred line LH172.

The closest prior art to LH172 is the parental line LH82.

LH172 has a much improved stalk quality and root strength when compared to LH82. LH172 unexpectedly has good late season stay green characteristics, along with good resistance/tolerance to the combination of diseases of Northern Leaf Spot, Southern Leaf Blight and Gray leaf spot. LH172 has an open husk at the tip of the ear which may partially explain its fast dry down characteristic. Fast dry down is an especially important trait in cool, slow growing seasons, which most of the U.S. corn belt experienced during 1992. Hybrids involving LH172 can be grown further South (in the southern portion of maturity zone seven), than would be expected.

TABLES

In the tables that follow, the traits and characteristics of inbred corn line LH172 are given in hybrid combination. The data collected on inbred corn line LH172 is presented for the key characteristics and traits. The tables present yield test information about LH172. LH172 was tested in several hybrid combinations at eight locations, with two or three replications per location. Information about these hybrids, as compared to several check hybrids, is presented.

The first pedigree listed in the comparison group is the hybrid containing LH172. Information for the pedigree includes:

1. Mean yield of the hybrid across all locations.

2. A mean for the percentage moisture (% M) for the hybrid across all locations.

3. A mean of the yield divided by the percentage moisture (Y/M) for the hybrid across all locations.

4. A mean of the percentage of plants with stalk lodging (% SL) across all locations.

5. A mean of the percentage of plants with root lodging (% RL) across all locations.

6. A mean of the percentage of plants with dropped ears (% DE).

7. The number of locations indicates the locations where these hybrids were tested together.

The series of hybrids listed under the hybrid containing LH172 are considered check hybrids. The check hybrids are compared to hybrids containing the inbred LH172.

The (+) or (-) sign in front of each number in each of the columns indicates how the mean values across plots of the hybrid containing inbred LH172 compare to the check crosses. A (+) or (-) sign in front of the number indicates that the mean of the hybrid containing inbred LH was greater or lesser, respectively, than the mean of the check hybrid. For example, a +4 in yield signifies that the hybrid containing inbred LH172 produced 4 bushels more corn than the check hybrid. If the value of the stalks has a (-) in front of the number 2, for example, then the hybrid containing the inbred LH172 had 2% less stalk lodging than the check hybrid.

                  TABLE 1                                                          ______________________________________                                         Overall Comparisons of                                                         LH172 × LHE136 Hybrid Vs. Check Hybrid                                            Mean                                                                  Hybrid   Yield    % M     Y/M  % SL  % RL  % DE                                ______________________________________                                         LH172 ×                                                                           150      14.73   10.19                                                                               3     0     1                                   LHE136                                                                         (at 15 Loc's)                                                                  as compared                                                                    to:                                                                            LH192 ×                                                                           -13      -1.09   -.12 0     0     0                                   LH82                                                                           LHE136 ×                                                                          -9       -1.05   +.13 0     0     0                                   LH82                                                                           LH132 ×                                                                           -4       -.79    +.26 +1    0     0                                   LH181                                                                          ______________________________________                                    

                  TABLE 2                                                          ______________________________________                                         Overall Comparisons of                                                         LH172 × LH202 Hybrid Vs. Check Hybrid                                             Mean                               %                                  Hybrid   Yield    % M     Y/M   % SL  % RL  DE                                 ______________________________________                                         LH172 ×                                                                           165      15.27   10.80  4     0     1                                 LH202                                                                          (at 16 Loc's)                                                                  as compared                                                                    to:                                                                            LH202 ×                                                                           -5       -1.31   +.58  -1    -1    +1                                 LH181                                                                          LH202 ×                                                                           +6       -.97    +1.00  0    -1    +1                                 LH127                                                                          LH202 ×                                                                           +1       -.85    +.66  -1    -1    +1                                 LH82                                                                           LH74 ×                                                                            +1       -.25    +.24   0     0    +1                                 LH181                                                                          LH74 ×                                                                            +9       -.05    +.63  -1    -1     0                                 LH82                                                                           ______________________________________                                    

                  TABLE 3                                                          ______________________________________                                         Overall Comparisons of                                                         LH172 × LH74 Hybrid Vs. Check Hybrid                                              Mean                                                                  Hybrid   Yield    % M     Y/M  % SL  % RL  % DE                                ______________________________________                                         LH172 ×                                                                           153      16.23   9.42  5     0    0                                   LH74                                                                           (at 16 Loc's)                                                                  as compared                                                                    to:                                                                            LH202 ×                                                                           -4       -1.78   +.70 -1    -3    0                                   LH82                                                                           LH74 ×                                                                             0       -.93    +.51 +1     0    0                                   LH181                                                                          LH74 ×                                                                            +1       -.22    +.17  0    -1    0                                   LH82                                                                           LH74 ×                                                                            +11      +.18    +.56 +1    -5    0                                   LH61                                                                           ______________________________________                                    

                  TABLE 4                                                          ______________________________________                                         Overall Comparisons of                                                         LH172 × LH146 Hybrid Vs. Check Hybrid                                             Mean                                                                  Hybrid   Yield    % M     Y/M  % SL  % RL  % DE                                ______________________________________                                         LH172 ×                                                                           169      19.19   8.82  4     2    0                                   LH146                                                                          (at 16 Loc's)                                                                  as compared                                                                    to:                                                                            Pioneer 3751                                                                            -7       +.45    -.61 +0    +1    -1                                  LH146 ×                                                                           +15      +.80    +.42 -1    -1    0                                   LH82                                                                           LH74 ×                                                                            +11      +.88    +.20 -1    +2    0                                   LH85                                                                           LH206 ×                                                                           +14      +1.06   +.27 0     +2    0                                   LH85                                                                           LH163 ×                                                                           +19      +1.19   +.47 +1    +1    0                                   LH146                                                                          ______________________________________                                    

DEPOSIT INFORMATION

Inbred seeds of LH172 have been placed on deposit with the American Type Culture Collection (ATCC), Rockville, Md. 20852, under Deposit Accession Number 75314 on Sep. 25, 1992. A Plant Variety Protection Certificate is being applied for with the United States Department of Agriculture.

Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity and understanding, it will be obvious that certain changes and modifications may be practiced within the scope of the invention, as limited only by the scope of the appended claims. 

What is claimed is:
 1. An inbred corn seed designated LH172 having ATCC deposit No.
 75314. 2. A corn plant produced by growing the seed of claim
 1. 3. Pollen of the plant of claim
 2. 4. An ovule of the plant of claim
 2. 5. An inbred corn plant with all the physiological and morphological characteristics of the corn plant of claim
 2. 6. A tissue culture comprising regenerable cells of the plant of claim
 2. 7. A corn plant regenerated from the tissue culture of claim 6, wherein said plant has all the physiological, and morphological characteristics of the plant of claim
 2. 8. A method to produce a hybrid corn seed comprising the steps of:a) planting in pollinating proximity seeds of corn inbred line LH172 and another inbred line; b) cultivating corn plants resulting from said seeds until said plants bear flowers; c) emasculating the male flowers of the plants of either inbred line; d) allowing cross pollination to occur between said inbred lines; and, c) harvesting seeds produced on said emasculated plants of the inbred line.
 9. A first generation (F₁) hybrid corn plant produced by growing said hybrid corn seed of claim
 8. 